Carlsen accepts the pawn sac.
3... b8a6 Caruana keeps the c7-pawn protected. 4. d2d3  4... c7c6 Forever preventing Nb5, but the position of the knight on b6 is weakened. 5. c1e3 Immediately exploiting the problems with Black's last move. 5... g7g5 The best chance to create counterplay. Caruana undoubtedly had prepared this move in advance.